(CNN) -- Taliban militants took control Wednesday of a district 60 miles away from the Pakistani capital of Islamabad.

CNN's Peter Bergen says an unstable Pakistan is more dangerous than an unstable Afghanistan.

The militants said they took control of the Buner district to ensure that Islamic law, or sharia, is properly imposed. The Pakistani government called the advance into Buner a breach of a recently signed peace agreement.

"Both Pakistani politicians and the military don't really have a strategy on how to deal with this," CNN national security analyst Peter Bergen said on CNN's "American Morning." "The Taliban are exploiting this and the full economic situation in Pakistan to gain even larger swaths of territory."

During a conversation on Monday with CNN's Manav Tanneeru, Bergen spoke about Pakistan's historic and current impact on the politics of Afghanistan.

The interview has been edited for length and clarity.

CNN: Earlier this year, when President Obama approved more troops for Afghanistan, he coupled that with aid for Pakistan. Why should Americans care about Pakistan when the fighting is actually happening in Afghanistan?

Bergen: Pakistan is where the Taliban are headquartered. Pakistan is where al Qaeda is headquartered. Pakistan has nuclear weapons. Pakistan has proliferated nuclear weapon technologies to other rogue states. And it's also going to be the fifth largest country in the world with 175 million people today and perhaps 200 million people by 2015.

If this country breaks up or if the militants were to take over -- which I think is a very distant proposition, even with all the things that have happened -- that is a much bigger deal than Afghanistan, which doesn't have nuclear weapons, which doesn't have the headquarters of the Taliban and the headquarters of al Qaeda. The stakes are higher in Pakistan.

Speak a bit about the Pakistan role in Afghanistan from a historical perspective. How far back does the relationship go?

"Pakistan has long had an involvement in Afghanistan. Obviously, that really picked up with the Soviet invasion of Afghanistan. The United States and allies like Saudi Arabia funneled money to the Afghan Mujahedin movements, but where that money went was controlled by the Pakistani military and its intelligence agency, the ISI.

As a result, the ISI made a lot of key decisions on which Afghan Mujahedin movements were to fund. They tended to support the ones they felt most fulfilled their strategic objectives, which were Pashtun Islamists like Gulbuddin Hekmatyar. When the Soviets withdrew, they switched horses and put their money on the Taliban. See who's who in Afghanistan »

Now, why would they put their money on the Taliban? Pakistan has a doctrine of strategic depth, which they have had for decades. It says that, in the event that India invades Pakistan over their eastern border, they want to have a pro-Pakistani state on their western border, so that they don't have to worry about two fronts. That doctrine remains in place.

Now, of course, the Pakistani Taliban has turned against the Pakistani state.

You refer to a Pakistani Taliban. How is that different from what we've traditionally seen as the Taliban?

I think the Pakistani Taliban is a little bit different from the Afghan Taliban. The Afghan Taliban, led by Mullah Omar, has made it clear fairly often that the Pakistani government is not the main enemy. The main enemy is the U.S. and NATO forces in Afghanistan.

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The Afghan Taliban, which is headquartered in Pakistan, doesn't want to antagonize the Pakistani government. The Pakistani Taliban seems to have taken a different tack.

How would you characterize Pakistan's current relationship with Afghanistan? The question is on two levels: The first is between the two legitimate governments and the other is on the shadow level.

I think the civilian governments on both sides share a lot in common. They're both opposed to violent, Islamist fundamentalists. The problem with Pakistan is that you've got a weak elected civilian government and a strong unelected military government that continues to have veto power over national security policy. I think there is a lot of common interest between the two Pakistani and Afghan governments, at least in theory, because I think everyone sort of realizes that the militants are really a potential threat to both governments.

But then you do have the attack on the Indian embassy in Kabul. Both Afghan and American officials asserted that some elements of the ISI were somehow involved. It's hard to know how far up the chain of command that goes. I don't know the answer to that question.

I don't think the Pakistani establishment knows what they're going to do with this problem, and when I say the establishment, I mean the political military establishment. I don't think they have a real plan. I think they're surviving day-to-day.

What's your sense of U.S.-Pakistani cooperation on that front?

I think there is some degree of cooperation because, clearly, the drone strikes are done with Pakistani intelligence on the ground. And despite whatever the Pakistani politicians say, some of the drones appear to be leaving Pakistani air bases. I think there is a fair amount of cooperation on that.

What options does the U.S. have other than the predator drone strikes?

I think the options are very limited. The U.S. has some leverage in Pakistan, but it doesn't [have the option] of occupying Pakistan and it never will. I think the problem is not that the U.S. doesn't have a strategy to deal with the militants. I think the problem is that the Pakistanis don't really have a coherent strategy. If they don't have a coherent strategy, it's really hard for the United States to support their strategy. They waver between essentially military expeditions and appeasement, and neither is very successful.

And the U.S. can't simply invade the border areas?

The only circumstance under which that would even be remotely possible is if there was another major terrorist attack in the U.S. that was traceable to the federally administered tribal areas [in Pakistan.]

There would be a great deal of pressure from the American public to do something about it directly, even if it was understood by the American political military establishment that such a move be counter-productive.

And that's why the drone program is happening. It's both a tactical success and probably a strategic error, but in the absence of any other [option]...

Why is it a "potential strategic error?"

The jury's out, but what happens is that all the militants move into the [tribal areas] and then they move further into Pakistan because they're trying to escape these strikes, and they further destabilize the Pakistani state. At the end of the day, an unstable Pakistan is more of a strategic error for the United States than an unstable Afghanistan.